Off-line channel tuning amplitude slope matched filter architecture

Abstract

A tuning control system and associated method is provided for continuously and automatically tuning a lobed amplitude slope matching filter (ASMF) to a band center of an interfering signal to provide improved rejection of an interfering signal coupled from a transmission antenna into a local receive antenna in the presence of local multi-path, thereby Providing improved interference cancellation system performance. The tuning control system is provided as an element of an interference cancellation system.

1. A method for continuously and automatically frequency tuning a variable lobe filter structure (VLFS) to an inserted signal to allow tracking of the inserted signal to match a dynamically changing amplitude slope of a second signal using an offline process for improved interference cancellation system performance, the method comprising:
 a) forming a first broadband RF lobed filter having a quiescent null proximate to and offset above a center frequency of an imaginary broadband RF lobed tuning filter; 
 b) forming a second broadband RF lobed filter having a quiescent null proximate to and offset below the center frequency of the imaginary broadband RF lobed tuning filter; 
 c) detecting a level of RF energy output from the first broadband RF lobed filter as a first broadband RF lobed filter output; 
 d) detecting a level of RF energy output from the second broadband RF lobed filter as a second broadband RF lobed filter output; 
 e) calculating an error signal by subtracting the first broadband RF lobed filter output value from the second broadband RF lobed filter output value; 
 f) integrating the error signal to generate a control voltage; 
 g) dynamically adjusting the delay time T, via the generated control voltage, to control a lobe bandwidth of the first and second broadband RF lobed filters, an imaginary nulling RF lobed filter and the imaginary broadband RF lobed tuning filter; 
 h) forming a more narrowband RF lobed filter orthogonal to the imaginary broadband RF lobed nulling filter in its quiescent state, 
 i) skewing the narrowband RF filter lobe to implement a corrective amplitude slope of the inserted signal, thereby improving the performance in the improved interference cancellation system; and 
 (j) repeating steps (a)-(i). 
 
     
     
       2. The method of  claim 1 , wherein the first broadband RF lobed filter is formed from a second signal path having a delay of T−ΔT relative to a first signal path forming the imaginary broadband. RF lobed tuning filter having a delay T. 
     
     
       3. The method of  claim 1 , wherein the second broadband RF lobed filter is formed from a third signal path having a delay of T+ΔT relative to a first signal path forming the imaginary broadband RF lobed tuning filter having a delay T. 
     
     
       4. The method of  claim 1 , wherein quiescent nulls of the first and second RF lobed filters bracket a quiescent null of an imaginary lobed nulling filter that is orthogonal to the imaginary RF lobed tuning filter. 
     
     
       5. The method of  claim 1 , wherein the step (g) of dynamically adjusting the delay time T via the generated control voltage indirectly controls the frequency of the first and second broadband RF lobed filter quiescent nulls to effectively bracket the inserted signal to be tracked. 
     
     
       6. The method of  claim 1 , wherein the step (g) of dynamically adjusting the delay time T is a continuous process. 
     
     
       7. The method of  claim 1 , wherein the step (g) of dynamically adjusting the delay time T is a discreet process. 
     
     
       8. The method of  claim 1 , where the value of ΔT is selected to provide sufficient offset of first and second broadband RF lobed filter quiescent nulls such that they are separated by the expected bandwidth of the inserted signal to be tracked. 
     
     
       9. The method of  claim 1 , further comprising forming the more narrowband RF lobed filter dependent upon the tuning of the broadband RF lobed filters. 
     
     
       10. The method of  claim 1 , wherein the more narrowband RF lobed filter is orthogonal to the imaginary broadband RF lobed nulling filter in its quiescent state. 
     
     
       11. The method of  claim 10 , wherein one of said plurality of lobes is peaked on the interfering signal to be tracked. 
     
     
       12. The method of  claim 1 , wherein said narrowband RF lobed filter is comprised of a plurality of lobes within a single lobe of the imaginary broadband RF tuning filter. 
     
     
       13. The method of  claim 1 , wherein the step of skewing the narrowband RF filter lobe at said step (i) is performed under the control of an external amplitude slope control signal. 
     
     
       14. The method of  claim 13 , wherein said one of said plurality of lobes peaked on the inserted signal to be tracked is a quiescent lobe of an amplitude sloped matching filter (ASMF) function. 
     
     
       15. The method of  claim 13 , wherein said one of said plurality of lobes peaked on the interfering signal to be tracked is centered at a null of the imaginary broadband RF lobed nulling filter. 
     
     
       16. The method according to  claim 1 , wherein the step (g) of dynamically adjusting a delay time (T) for tuning the quiescent nulls of the formed first and second broadband RF lobed filters further comprises skewing the first and second broadband RF lobed filter quiescent nulls in a direction to effectively evenly match energy of the tracked interfering signal passing through the two filters. 
     
     
       17. The method according to  claim 16 , wherein the control process comprises:
 a) measuring an RF energy output from the pair of broadband RF filters; 
 b) subtracting energy measurement value of first RF filter from measurement value of second RF filter; 
 c) amplifying and integrating the error signal (difference of the RF energy output measurement values from the broadband RF filters). 
 d) using the integrated error signal to change the value of T controlling filter delays. 
 
     
     
       18. The method according to  claim 1 , wherein the step (g) of dynamically adjusting a delay time is performed via a control process. 
     
     
       19. The method of  claim 18 , wherein narrowing the filter lobes results in a downward frequency shift of the individual lobes and nulls of the of the more narrowband RF lobed filter. 
     
     
       20. The method of  claim 1 , wherein increasing the control voltage causes the delay T to be increased resulting in a narrowing of the filter lobes of the more narrowband RF lobed filter. 
     
     
       21. The method of  claim 20 , wherein widening the filter lobes results in an upward frequency shift of the individual lobes and nulls of the of the more narrowband RF lobed filter. 
     
     
       22. The method of  claim 1 , wherein decreasing the control voltage causes the delay T to be decreased resulting in a widening of the filter lobes of the more narrowband RF lobed filter. 
     
     
       23. The method according to  claim 1 , wherein the first and second broadband RF lobed filters have a null to null bandwidth substantially twice the desired tuning bandwidth.